He said claims made by Northern Ireland First Minister Arlene Foster that Dublin was trying to poach investment and undermine the North's economy were not helpful.

"I don't regard her comments as being helpful in the circumstances," Mr Flanagan said.

"I believe it's absolutely essential that we work together. This is a most serious challenge. There is the old clichè 'strength in unity'. If we divide, or if we engage in unhelpful activity, we will be the weaker."

Mr Flanagan has taken issue with remarks from Ms Foster at the DUP annual conference where she suggested the Republic was trying to poach post-Brexit business from Northern Ireland. Ms Foster blamed this on "fear and political instability".

Mr Flanagan said yesterday that an invitation to attend the forum had been sent to all political parties. But Ms Foster has repeatedly said she would not attend, ramping up her comments in recent days ahead of her party conference.

Ms Foster branded yesterday's event a grand-standing exercise and said she had better things to do than listen to "remoaners".

"I do believe it's a missed opportunity on the part of those who've indicated that they didn't intend being with us here today," Mr Flanagan said.

"However, there will be further opportunity, and I refer to the North South Ministerial Council and to a series of dialogues at bilateral level, given the range of institutions under the Good Friday Agreement."

Mr Flanagan said he has no plans to meet the first minister ahead of a meeting of the North South Ministerial Council in Armagh on November 18.

Northern Ireland First Minister Martin McGuinness, in a curious political twist, tried to downplay Ms Foster's position, saying he did not believe the unionist parties were not listening.

"I think they understand the seriousness of the situation that we are all facing, including they as elected representatives for the people that they represent," Mr McGuinness told yesterday's gathering in the Royal Hospital in Kilmainham.

"I know for a fact that unionists were shocked by the outcome of the Brexit referendum."

Wrapping up the gathering, Mr Flanagan said there would be a further conference early next year, with several sector-specific dialogues held in the interim.